Screen-based desktop videoconferencing, screen-based video presentations and screen-based digital television are now mature technologies, but the requirement for a screen is taxing in terms of space requirements, mobility, and cost. Using smart phones or tablet computers for mobile video conferencing allows for mobility but introduces the difficulty of holding a screen while moving, small image size and difficulty multi-tasking. More recently, augmented reality has become available as a way of presenting video or other image content. However, augmented reality headsets can be restrictive in some situations and can be difficult to use by novice users, or those with physical disabilities, the elderly and the very young. In the case of augmented reality video conferencing, augmented reality headsets impede the view of the face of both participants if both use headsets, or one participant if that person is not wearing a headset.
The embodiments described below are not limited to implementations which solve any or all of the disadvantages of known projection units.